Most conventional motorized vehicles include a powertrain with a power source, such as an internal combustion engine or ICE, connected to a power transmission adapted to manipulate and transmit power from the engine to a final drive system (e.g., driveshaft, differential, and wheels.) Some transmissions include a hydrodynamic input device, such as a torque converter, positioned between the engine and the transmission. The torque converter is a hydrokinetic fluid coupling employed predominantly to allow the engine to run without stalling when the vehicle wheels and transmission gears come to a stop, and to provide torque multiplication in the lower speed range of the engine. Certain torque converter assemblies integrate a torque converter clutch (TCC), also known as a lockup clutch, to provide a bypass mechanism, allowing the engine to circumvent the torque converter and transmit power directly to the transmission.
As a result of intermittent combustion and cyclical piston motion, ICEs may generate torsionals or vibrations during normal operation that are undesirable to transmit to the vehicle transmission. The degree of engine torsional excitation is typically exacerbated in proportion with the number of cylinders. ICEs equipped with displacement-on-demand functionality can selectively deactivate certain engine cylinders to save on fuel. This mode of operation may produce distinctive (or inconsistent) torque fluctuations from the engine operating on all cylinders. Finally, an ICE may also generate compression pulses during startup and shutdown operations.
To isolate and counteract the unwanted torsionals generated by the engine, various damper systems have been implemented into the powertrain system. These dampers are generally packaged between the engine's output shaft (e.g., crankshaft) and the input shaft of the transmission (e.g., turbine shaft.) Some damping devices are configured with coil springs that have the capacity to carry maximum engine torque plus some margin above. To this regard, the lockup clutch may include elongated arc-shaped, circumferentially extending springs that are compressed when a shock or torsional vibration occurs during a lockup operation, i.e., engagement of the lockup clutch.
In hybrid-type vehicles (e.g., a vehicle configured with a powertrain using one or more electric motors individually or in concert with an ICE for propulsion), the hybrid ICE typically operates at lower speeds more often than in traditional automobiles, and can be turned on and off while the hybrid vehicle is being propelled by the electric motor(s). Consequently, the ICE in hybrid vehicles may be subjected to startup and shutdown operation more frequently than engines used in non-hybrid powertrains. Much like its traditional counterpart, the hybrid ICE may generate compression pulses during starts and stops that can produce undesirable vibration in hybrid vehicles.